"At this time, we don't know who they are," he said. "We believe the shooter committed suicide at the scene but we're not positive."

About nine others were believed wounded, WTAE quoted police as saying. One hospital representative told the channel that five women were being treated for multiple gunshots and were in critical condition.

A witness identified as Nicole told WTAE that the killer walked into an all-female dance class carrying a bag, turned off the lights, and began shooting from at least one firearm, which police said was a handgun.

"He got off a lot of shots," Nicole said. "People everywhere were screaming. It was horrible."

She said that about 30 women were in the dance room during the evening class, while WTAE's reporter said that about 100 people may have been present in the gym in total.

"I turned around there was one girl shot in the thigh and one girl shot in the back," said Branson Holly, who was taking another class at the gym at the time.

"I'm still shaken because I was in spinning class and it could have been my class," Holly said.

"I could see flashes in the dark and that's when I realized that someone was actually shooting," another visitor to the gym told a telelvision reporter.

WTAE showed footage of ambulances and police cars flooding into the area, which is part of a shopping center.

Gun violence regularly plagues the United States, with incidents just this year including rampages at an immigration center in New York state, the Holocaust museum in Washington, and a theater in Georgia, as well as a spree in Tennessee and Alabama.